The present invention relates to radiation imaging systems, and in particular, to solid state X-ray radiation imaging systems capable of operating in multiple detection and display modes.
The use of X-ray radiation has become a valuable and widespread tool in medical diagnoses and treatments. In film radiography, a burst of X-rays, after passing through the body, is recorded on high resolution X-ray film. In fluoroscopy, an image intensifier tube converts X-ray radiation to a video signal for viewing and recording interior body activity as a video image.
Film radiography is commonly used due to its good spatial resolution, high signal-to-noise ratio (SNR), large detection area and low cost. However, developing exposed X-ray film typically takes a minimum of ninety seconds which can be too long in emergency situations. Further, the relatively low dynamic range of X-ray film can result in under- or over-exposed images and, therefore, necessitate additional exposures which increase the aforementioned time delay as well as the X-ray dosage received by the patient
The image intensifier tube used in fluoroscopy has a greater exposure latitude than X-ray film, but also has a more limited active detection area and lower spatial resolution. The lower spatial resolution associated with the total active area is somewhat mitigated in that the image intensifier tubes allow magnification of the central image portion, thereby providing a means to enhance visual details. However, the image intensifier tube is typically heavy, bulky and expensive, and can introduce image distortion which can only be partially removed during post processing.
A number of alternative X-ray imaging technologies have been developed. For example, one alternative, known as computed radiography, involves the use of a photostimulable phosphor plate which has the same physical appearance as a standard X-ray film cassette and provides good spatial resolution, SNR and dynamic range. However, after exposure to X-rays, the photostimulable phosphor plate must be scanned with a laser system which is large and expensive, and the readout process is just as slow as the development of film.
Another alternative which provides good spatial resolution and dynamic range, as well as the added advantage of compatibility with real time digital image processing techniques, involves the use of solid state detector panels. One such panel uses an amorphous silicon (a-Si) detector array arranged as a two dimensional matrix of pixels, each of which consists of a photosensitive element and a transistor switch. As with X-ray film cassettes, the detector array is covered with a scintillation layer to convert impinging X-rays into visible light for the photosensitive elements.
An X-ray imaging system in accordance with the present invention is capable of operating in multiple imaging modes, such as radiographic and fluoroscopic, while providing spatial resolutions, SNRs and dynamic ranges which can be selectively optimized to the selected mode of operation.
In accordance with one aspect of the present invention, the combining of pixel information collected by the detector array, i.e., xe2x80x9cpixel binning,xe2x80x9d is performed by selectively combining one portion of the pixel information within the detector array and selectively combining the remainder of the pixel information within the circuits fed by the output of the detector array. Such pixel binning is preferably analog in nature and is performed prior to any digitizing of the pixel signals, thereby providing for a higher SNR, and, importantly, reducing the bandwidth requirements for the digital electronics. More specifically, a multiple mode X-ray detector system for supporting multiple X-ray image display modes by providing X-ray image signals having selectable spatial resolutions includes a detector array and a group of detector array receiver circuits. The detector array is configured to receive a group of detector control signals and in accordance therewith receive and convert X-ray photons corresponding to a two-dimensional image into a first group of image signals representing a first two-dimensional array which includes a first group of rows and a first group of columns of pixels which together correspond to the two-dimensional image and which individually correspond to respective portions of the two-dimensional image. The detector array provides, in accordance with the detector control signals, a second group of image signals representing a second two-dimensional array which includes a second group of rows and the first group of columns of super pixels which selectively represent respective individual ones or multiple adjacent ones of the first group of rows of pixels and respective individual ones of the first group of columns of pixels, respectively. The detector array receiver circuits, coupled to the detector array, are configured to receive a group of receiver control signals and in accordance therewith receive and combine the second group of image signals and in accordance therewith provide a third plurality of image signals representing a third two-dimensional array which includes the second group of rows and a second group of columns of super pixels which selectively represent respective individual ones of the second group of rows of super pixels and respective individual ones or multiple adjacent ones of the first group of columns of super pixels, respectively.
In accordance with another aspect of the present invention, data flags are used to identify defective pixels within the detector array and are inserted into the data stream collected from the detector array for dynamic processing along with the pixel data. More specifically, a data processing system for processing a serial stream of multiple bit data sets which represent an array of pixels corresponding to a two-dimensional image including correcting for defective pixels individually or in groups includes a data processing circuit and a data selection circuit. The data processing circuit is configured to receive and process together a plurality of successive sets of image data with a corresponding plurality of successive sets of correction data and in accordance therewith provide a plurality of successive sets of corrected image data. The plurality of successive sets of image data represents a plurality of pixels corresponding to a two-dimensional image, the plurality of successive sets of correction data represents a plurality of correction factors, each one of the plurality of correction factors corresponds to a respective one of the plurality of pixels and each one of the plurality of successive sets of correction data includes a data subset which indicates whether the respective one of the plurality of pixels is defective. The data selection circuit, coupled to the data processing circuit, is configured to receive and select between individual ones of the plurality of successive sets of corrected image data and individual ones of the corresponding plurality of successive sets of correction data and in accordance therewith provide a plurality of successive sets of selected data. An individual one of the plurality of successive sets of selected data includes a corresponding individual one of the plurality of successive sets of correction data when the data subset indicates that the corresponding respective one of the plurality of pixels is defective, and the individual one of the plurality of successive sets of selected data includes a corresponding one of the plurality of successive sets of corrected image data when the data subset does not indicate that the corresponding respective one of the plurality of pixels is defective.
In accordance with still another aspect of the present invention, a data buffer and filter is used to perform still image capture during radiographic imaging and to recursively filter incoming image data during fluoroscopic imaging. More specifically, a digital data buffer and filter for selectively storing image pixel data, combining new incoming image pixel data with previously stored image pixel data and providing such combined image pixel data for display thereof in a still image mode or an image motion mode includes a data scaling and summing circuit and a data memory circuit. The data scaling and summing circuit is configured to receive and scale an input data signal, receive and scale a stored data sum signal and sum said scaled input data signal and said scaled stored data sum signal and in accordance therewith provide a data sum signal. The input data signal is scaled in accordance with a first scaling factor and the stored data sum signal is scaled in accordance with a second scaling factor. The input data signal includes a plurality of successive sets of image data, and each one of the plurality of successive sets of image data includes a plurality of pixel data with active and inactive data states and which corresponds to a two-dimensional image having a two-dimensional array including a plurality of rows and a plurality of columns of pixels which together correspond to the two-dimensional image and which individually correspond to respective portions of the two-dimensional image. The data memory circuit, coupled to the data scaling and summing circuit, is configured to receive and selectively store the data sum signal and provide the stored data sum signal. The data scaling and summing circuit and the data memory circuit cooperatively operate in one of a plurality of operational modes during reception of the plurality of successive sets of image data. In a first one of the plurality of operational modes (e.g., in fluoroscopic mode), the first scaling factor has a value which is between zero and unity, and the second scaling factor has a value which equals a difference between unity and the first scaling factor value. In a second one of the plurality of operational modes (e.g., in radiographic mode): the first scaling factor has a value which is initially unity when a first one of the plurality of successive sets of image data is in the inactive data state, remains unity when a subsequent second one of the plurality of successive sets of image data is in the active data state and becomes zero when a further subsequent third one of the plurality of successive sets of image data is in the inactive data state; and the second scaling factor has a value which is initially zero, becomes unity when the subsequent second one of the plurality of successive sets of image data is in the active data state and remains unity thereafter.
These and other features and advantages of the present invention will be understood upon consideration of the following detailed description of the invention and the accompanying drawings.